U.S. patent application number 10/242905 was filed with the patent office on 2003-03-13 for warming blanket having remote safety circuit.
Invention is credited to Alvite, Armando, Horey, Leonard I., Kohn, Gabriel.
Application Number | 20030047556 10/242905 |
Document ID | / |
Family ID | 31991508 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047556 |
Kind Code |
A1 |
Horey, Leonard I. ; et
al. |
March 13, 2003 |
Warming blanket having remote safety circuit
Abstract
One or more current sensors are mounted externally of a heating
member so as to simplify construction of the heating member. The
sensors are particularly useful in safety control circuits for
heating members using PTC wire as resistance heating elements.
Inventors: |
Horey, Leonard I.; (Boca
Raton, FL) ; Alvite, Armando; (Miami, FL) ;
Kohn, Gabriel; (Boca Raton, FL) |
Correspondence
Address: |
Lawrence J. Shurupoff
Sunbeam Products, Inc.
2381 Executive Center Drive
Boca Raton
FL
33431
US
|
Family ID: |
31991508 |
Appl. No.: |
10/242905 |
Filed: |
September 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60318999 |
Sep 11, 2001 |
|
|
|
Current U.S.
Class: |
219/497 ;
219/212 |
Current CPC
Class: |
H05B 3/342 20130101;
H05B 2203/02 20130101; H05B 2203/014 20130101; H05B 2203/003
20130101; H05B 2203/016 20130101; H05B 1/0272 20130101; H05B
2203/017 20130101 |
Class at
Publication: |
219/497 ;
219/212 |
International
Class: |
H05B 001/02; H05B
003/34 |
Claims
What is claimed is:
1. A heating assembly, comprising: a pliable cover; a heating
element provided within said cover; and a safety circuit located
externally of said cover for controlling power supplied to said
heating element; said circuit comprising at least one sensor for
detecting electrical current supplied to said heating element and
generating an output signal.
2. The assembly of claim 1, wherein said cover comprises a
blanket.
3. The assembly of claim 1, wherein said sensor comprises a
coil.
4. The assembly of claim 1, wherein said heating element comprises
PTC wire.
5. The assembly of claim 1, further comprising a power cord having
a wall plug, and wherein said safety circuit is mounted on said
wall plug.
6. The assembly of claim 1, further comprising an ASIC receiving
said output signal and producing a control signal.
7. The assembly of claim 6, further comprising a controller
receiving said control signal.
8. The assembly of claim 1, further comprising a controller, and
wherein said safety circuit is carried by said controller.
9. The assembly of claim 1, wherein said at least one sensor
comprises a pair of sensors, which produce a pair of output voltage
signals.
10. The assembly of claim 9, further comprising an ASIC receiving
and processing said output signals to produce a control signal.
11. The assembly of claim 1, further comprising an ASIC receiving
said output signal and producing a control signal and a gain
resistor connected to said ASIC for adapting said ASIC to a
specific application.
12. The assembly of claim 1, further comprising an ASIC receiving
said output signal and producing a control signal and a voltage
divider connected to said ASIC for adapting said ASIC to a specific
application.
Description
[0001] This application claims the benefit of U.S. Provisional
Application Serial No. 60/318,999 filed Sep. 11, 2001.
FIELD OF THE INVENTION
[0002] The present invention relates to electric heating blankets,
pads and pillows.
DESCRIPTION OF PRIOR DEVELOPMENTS
[0003] Present day warming blankets typically include a safety
circuit for interrupting or cutting off electrical power to the
blanket in the event of an electrical fault such as arcing, a short
circuit or an open circuit.
[0004] Conventional safety circuits measure voltage at the remote
end of the heating wire, i.e., the end farthest from where the wire
enters the blanket. This form of measurement requires a safety
circuit module to be located inside the blanket or an additional
pair of wires must be returned to the controller located on the
exterior of the blanket. This requires the heating wire to complete
a full circuit loop within the blanket and return back to the edge
of the blanket where the resistance heating wire is connected to an
external power cord. This connection requires an additional
electrical connector pin or pins.
[0005] It would be advantageous to be able to externally measure
only the current entering a warming blanket or pad in order to
detect an electrical fault in the resistance/heating wire. This
would be particularly advantageous in the case of resistance wire
fabricated from PTC (positive temperature coefficient) wire. In
this case a complete looped circuit would not be required and a
simplified and more economical blanket construction would be
enabled.
[0006] In any case, by measuring the current entering the blanket,
a safety circuit can be located remotely and externally of the
blanket.
SUMMARY OF THE INVENTION
[0007] The invention has been developed to fulfill the needs noted
above. A primary object of the invention is to provide an electric
fault detector positioned externally from a heating blanket without
the need for extending one or more wires back to the external
controller. This object is achieved by locating most of the fault
detecting electronics in an application specific integrated circuit
(ASIC). This reduces both the safety circuit size and its cost.
[0008] The resulting safety circuit can be located on a controller
or near an electrical connector, i.e., near a wall plug, if
desired. The combination of the safety circuit and the wall plug
can be molded as a single compact module, if desired. By
positioning the safety circuit at the wall plug and measuring
electrical faults at this point, faults between the wall plug and
blanket can be immediately detected, i.e., faults in the power
cord. Prior safety circuits located at the blanket could not detect
such faults.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic circuit diagram of a safety circuit
constructed in accordance with the invention;
[0010] FIG. 2 is a view of an alternate sensor for use in the
circuit of FIG. 1;
[0011] FIG. 3 is a schematic top plan view showing a heating pad or
blanket constructed in accordance with the Prior Art;
[0012] FIG. 4 is an enlarged partial view of the portion of FIG. 3
enclosed in dashed lines; and
[0013] FIG. 5 is a view similar to FIG. 3 showing a blanket
constructed in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] The present invention will now be described in conjunction
with FIG. 1 which shows a safety circuit 10 including an
application specific integrated circuit or ASIC 12. In the example
shown, the ASIC is a custom CMOS ASIC. If desired, discrete
components can be mounted on a circuit board instead of using an
ASIC. However, an ASIC is preferred because of its compact size and
ability to be packaged as a small unobtrusive module or chip.
[0015] Each power wire 16, 18 on power wall plug 20 extends through
a small current sensor 22, 24. The current sensors 22, 24 produce a
voltage output when current flows through the respective power
wires 16, 18. These voltages, IN1 and IN2, are input into the ASIC
12. The current sensors are preferably coils, i.e., ferrite
toroids, but can also be small resistors, 26, 28, i.e., 0.1 ohm, as
shown in FIG. 2. The voltage drop across the resistors produces a
similar voltage input signal to that produced by the sensors 22,
24.
[0016] The ASIC amplifies and processes the input signal(s) from
the current sensors 22, 24 (or 26, 28) and determines or calculates
an average sensor signal value based on the two inputs. However, if
desired, only one sensor 16 or 18 (or 26 or 28) can be used to
input a single voltage signal IN2. Two sensors are preferred for
the ability to detect a short circuit.
[0017] The resulting average (or single) voltage signal is
preferably offset by a predetermined amount set by an external
offset voltage 28 produced by a voltage divider 30 having resistors
29, 31. The average (or single) voltage signal is also preferably
amplified by a gain determined by, for example, an external 1%
resistor 32, for example. The resulting output control signal 34 is
sent through signal wire 35 is in the form of an analog voltage
signal which is proportional to the current in the line or power
cords 16, 18.
[0018] The analog voltage signal 34 is sent to a microcomputer 36
in a conventional controller 38. An analog to digital (A/D)
converter 40 located in the microcomputer 36, or elsewhere,
receives the analog voltage signal 34 and converts it to a digital
signal. The digital signal is processed by the microcomputer 36 to
monitor the current in the power cords 16, 18 and check for
abnormal current values which indicate a fault condition. A triac
50 in series with the line 18 allows the microcomputer 36 to
control power to the heating pad or blanket. When a fault condition
is detected, the controller switches off the power from power cords
16, 18 to the heating pad or blanket.
[0019] The entire safety circuit 10 can be located in the
controller 38 or externally of the controller 38 such as in power
cord plug 20. The safety circuit 10 includes the current sensors
22, 24, the ASIC 12 (or equivalent discrete components), the gain
resistor 32, the offset voltage setting resistors 29, 31 and a
small optional power supply 42 for powering the ASIC in the case
where the ASIC is mounted on plug 20.
[0020] When the safety circuit 10 is mounted by the wall plug 20,
the safety circuit is preferably molded with the wall plug 20 into
a single unitary plug assembly or module. In this case, three wires
would extend from the plug module to the blanket controller 38,
i.e., the two power wires 16, 18 and the safety signal wire 35.
[0021] A major advantage of the present invention is the ability to
use the same ASIC for controlling different sizes and types of
heating pads, blankets, pillows, etc. each having different current
flow characteristics. Instead of redesigning the ASIC, one need
only change the value of the external gain resistor 32 and/or the
values of the offset voltage resistor(s) 29, 31 in voltage divider
30 to adapt the ASIC for different control applications and to
optimize signal 35 for processing over the full useful input range
of controller 38.
[0022] Another advantage of the invention is the elimination of any
electronic components in the pad or blanket, since the circuit 10
can be located completely externally of the pad or blanket. This
facilitates blanket/pad assembly and removes bulky components from
the blanket/pad.
[0023] Another major advantage of the invention is the ability to
eliminate a return signal wire or wires 35 from the end of the
resistance wire which heats the blanket or pad. For example, as
seen in FIG. 3, the prior art heating blanket 50 has a serpentine
loop of PTC resistance wire 52 which terminates at an active safety
circuit module 54. When a predetermined voltage variation is
detected in wire 52 by module 54, a signal is sent to controller 38
via signal wire 35 to open switch 56 and terminate power to
resistance wire 52 in connector housing 58.
[0024] As seen in FIG. 4, module 54 can include one or more
resistors 60, 62 extending across power wires 16, 18 at the remote
end of wire 52. The base of transistor 64 is connected between the
resistors to send a go or no-go signal to signal wire 35 to control
the operation of switch 56. The module 54 complicates the assembly
of blanket 50 as does signal wire 35.
[0025] A much simpler to fabricate blanket assembly is shown in
FIG. 5 wherein module 54 and return wire 35 are eliminated from the
blanket construction and located remote from the blanket in
accordance with the invention. The safety circuit 10 of FIG. 1 can
be mounted on wall plug assembly or module 20, or the safety
circuit 10 can be mounted in controller 38, which can be mounted
adjacent or remote from the blanket 50.
[0026] Blanket 50 is shown for explanation purposes only. Blanket
50 can be any heating member, generally including a flexible,
pliable, soft and compliant cover made of a fabric or sheet
material, and a resistance wire held within the outer layers of the
cover.
* * * * *